Viscoelastic properties of colloidal gels

The microstructure and scaling of mechanical properties of dense colloidal gels were investigated as a function of volume fraction and strength of interparticle attraction. Gels were reversibly formed by cooling suspensions of octadecyl silica particles in decalin or tetradecane; Shear history independence of mechanical properties was ensured by preshearing the suspensions in the gelled state. Gelation resulted in suspensions with apparent fractal dimensions of 1.4. Shear densification resulted in an apparent fractal dimension of 2.5 for structures containing many particles. When the gelled suspension was presheared, just after the shear rate was set to zero, elastic moduli were small. Over time, the moduli recovered to a time independent value, G(infinity)', at a rate alpha. When measured over a wide range of volume fraction, phi, and strength of interparticle attraction, G(infinity)', alpha, and the strain limiting the extent of linear response to oscillatory deformations, gamma(M), fell onto master curves when plotted as a function of phi/phi(G) for 1.1 < phi/phi(G) < 5. Here phi(G) is the gel volume fraction that varied from 0.11 to 0.59 for temperatures studied. (C) 1997 The Society of Rheology.